The present invention relates in general to distance measuring and more specifically to a system and method using passive visual images to determine varying distances between aircraft during a refueling operation.
During air-to-air refueling operations between aircraft, a refueling operator must determine the distance between a refueling boom of the refueling aircraft and the receptacle on the receiving aircraft by visual determination. When the refueling boom is of the common tubular design, damage to the refueling boom or the receiving aircraft can result from inaccurate lineup of the boom nozzle with the receiving aircraft refueling receptacle. Damage as extensive as complete failure of the refueling boom has occurred in these situations.
Some refueling aircraft have one or more cameras installed, the camera images being relayed to viewing screens. Cameras improve the visibility of the refueling boom nozzle and improve the guidance of the boom nozzle to the receiving aircraft refueling receptacle. However, the use of cameras does not provide an accurate measurement of the constantly changing clearance dimension between the boom nozzle and the refueling receptacle. Therefore, the refueling operator must still rely on visual judgment of the clearance dimension, which can result in impacts between the boom nozzle and the receiving aircraft.
Systems are available which enable an aircraft refueling operator to accurately determine the distance between the refueling aircraft and a receiving aircraft. Common systems include laser range detection equipment. This type of equipment is not normally provided on aircraft and is an expensive addition as a backfit item to a refueling aircraft. In addition to the initial expense of these systems, maintenance time and expense is also required to keep the equipment in proper operating condition. Also, the use of laser range systems requires a laser source at or adjacent to the boom nozzle to provide the best indication of the changing clearance dimension to the refueling receptacle and a xe2x80x9chands-freexe2x80x9d operation so the refueling operator can operate the refueling boom control equipment. A laser source at the boom nozzle is susceptible to damage if the boom nozzle contacts the receiving aircraft.
It is therefore desirable to provide a low cost, minimum impact system for determining the distance between an aircraft refueling boom and a receiving aircraft refueling receptacle.
According to a preferred embodiment of the present invention, a distance measuring system for a refueling aircraft is disclosed which comprises at least one refueling boom, at least one camera, and a computer. The refueling boom is provided with a boom nozzle. The boom nozzle has a geometry suitable to matably connect with a receiving aircraft refueling receptacle. Each camera forms a plurality of images of both the boom nozzle and the refueling receptacle. The computer receives each of the images, converts the images to a plurality of pixels and analyzes the images to determine a distance between the boom nozzle and the refueling receptacle. The refueling boom has an attachment end for attachment to the refueling aircraft. The refueling boom attachment end forms a fixed reference point between the attachment end and the refueling aircraft. The attachment point of the camera to the aircraft also forms a camera reference point.
The fixed reference point of the refueling boom and the camera reference point are combined with known data including the length of the refueling boom and its extension angle in order to identify the location in space of the refueling boom nozzle relative to the refueling aircraft. This location in space is assigned coordinates using the pixel image of the boom nozzle.
A database of the computer is pre-loaded with a plurality of wire-frame models of various receiving aircraft (i.e., the aircraft to be refueled).The receiving aircraft type is either (1) manually selected by the equipment operator if known, or (2) automatically selected by the computer because its shape closely matches a receiving aircraft shape of one of the stored wire-frame models in the database of wire-frame models. Each wire-frame model has a plurality of digital coordinates assigned to identify key component locations. Each wire-frame model also contains information sufficient to identify a plurality of aspects, ranges, and locations of the aircraft.
The camera images of the receiving aircraft are digitized into images forming a plurality of pixels. Each of the plurality of pixels can be assigned coordinates. After the receiving aircraft type is selected, the selected database digital image is compared to the digitized camera image. The computer uses the data from the wire-frame model to identify an initial location, range, and aspect of the receiving aircraft. Once the initial location, range, and aspect are determined, the computer enters into a tracking mode which performs fast updates to the location, range, and aspect from further camera images. Each receiving aircraft position change is calculated by a change in pixel coordinates from each preceding camera image.
For each selected aircraft type, the refueling receptacle geometry and location coordinates are known. The spatial location of the receiving aircraft refueling receptacle is continuously updated and compared to the known boom nozzle location. A resulting distance between the boom nozzle and the receiving aircraft refueling receptacle is initially calculated and continuously recalculated until docking occurs.
Some refueling aircraft presently provide at least one camera to assist in the refueling operation and to assist the refueling boom operator in positioning the refueling boom relative to the receiving aircraft. If an analog type camera is employed on the refueling aircraft, the analog images from the camera need to be digitized. If one or more digital cameras are installed on the refueling aircraft, the digital images can be directly used by the computer.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.